Oh god that is really hard to decide...
One thing that comes immediately to mind is Big Brother. People being watched doing nothing really other than bitching around and figuring out ways to fuck with as little camera exposure as possible (although that might have changed since the first german season)
In terms of "scripted" television, i guess Full House wins. Unfunny and beyond annoying. And actually so bad that even the "Nostalgia Critic" Rant about it is painful: http://thatguywiththeglasses.com/videolinks/thatguywiththeglasses/nostalgia-critic/7511-fullhouse
Then again, what was the Show with this Steve Urkel Guy called again? While it was probably funnier than Full House, i remember how it departed from typical sitcom to annoyingly stupid fantasy bullshit. Ugh.